%QPSK与OQPSK
clear all;
close all;
M=4;
Ts=1;
fc=10;
N_sample=16;
N_num=100;
dt=1/fc/N_sample;
t=0:dt:N_num*Ts-dt;
T=dt*length(t);
py1f=zeros(1,length(t)); %功率谱密度1
py2f=zeros(1,length(t)); %功率谱密度2
for PL=1:100 %输入100段N_num个码字的波形,为了使功率谱密度看起来更平滑,
%可以取这100段信号功率谱的平均
d1=sign(randn(1,N_num));
d2=sign(randn(1,N_num));
gt=ones(1,fc*N_sample);
%QPSK调制
s1=sigexpand(d1,fc*N_sample);
s2=sigexpand(d2,fc*N_sample);
b1=conv(s1,gt);
b2=conv(s2,gt);
s1=b1(1:length(s1));
s2=b2(1:length(s2));
st_qpsk=s1.*cos(2*pi*fc*t)-s2.*sin(2*pi*fc*t);
s2_delay=[-ones(1,N_sample*fc/2) s2(1:end-N_sample*fc/2)];
st_oqpsk=s1.*cos(2*pi*fc*t)-s2_delay.*sin(2*pi*fc*t);
%经过带通后,再经过非线性电路
[f y1f]=T2F(t,st_qpsk);
[f y2f]=T2F(t,st_oqpsk);
[t y1]=bpf(f,y1f,fc-1/Ts,fc+1/Ts);
[t y2]=bpf(f,y2f,fc-1/Ts,fc+1/Ts);
subplot(221);
plot(t,y1);
xlabel('t');
ylabel('QPSK波形');
axis([5 15 -1.6 1.6]);
title('经过带通后的波形');
subplot(222)
plot(t,y2);
xlabel('t');
ylabel('OQPSK波形');
axis([5 15 -1.6 1.6]);
title('经过带通后的波形');
%经过非线性电路
y1=1.5*tanh(2*y1);
y2=1.5*tanh(2*y2);
[f y1f]=T2F(t,y1);
[f y2f]=T2F(t,y2);
py1f=py1f+abs(y1f).^2/T; %QPSK不同段信号功率谱密度相加
py2f=py2f+abs(y2f).^2/T; %OQPSK不同段信号功率谱密度相加
end
py1f=py1f/100;
py2f=py2f/100;
subplot(223);
plot(f,10*log10(py1f));
xlabel('f');
ylabel('QPSK功率谱密度(dB/Hz)');
axis([-15 15 -30 10]);
title('经过非线性电路后的功率谱密度');
subplot(224);
plot(f,10*log10(py2f));
xlabel('f');
ylabel('OQPSK功率谱密度(dB/Hz)');
axis([-15 15 -30 10]);
title('经过非线性电路后的功率谱密度');
figure(2)
x=-2:0.1:2;
y=1.5*tanh(2*x);
plot(x,y);
title('非线性电路的输入输出函数');